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United States Patent |
5,241,758
|
Cruz
,   et al.
|
September 7, 1993
|
Process for protecting surfaces against ambient particulate
contamination with the aid of blowing elements
Abstract
The blowing ramp formed by the blowing elements makes it possible to
maintain under an ultra-clean atmosphere the planar services of objects
during their transportion or conveying, whilst using a limited air flow;
the blowing elements are mainly constituted by a plate 2 having a central
orifice 6 facing which is located a pipe 4 supplied with ultra-clean air;
the process consists of placing the surface (11) of the object (10) at a
distance (d) of approximately 1 mm from the blowing surface (7). The flow
of air between these two surfaces is easily regulated in such a way as to
be laminar, thus providing protection against ambient particulate
contamination, which application may be applied to the conveying of
silicon wafers.
Inventors:
|
Cruz; Didier (Grenoble, FR);
Daval; Jacques (Meylan, FR);
Lazzari; Jean-Pierre (Corenc, FR);
Torrecillas; Francois (Saint Pancrasse, FR)
|
Assignee:
|
Commissariat a l'Energie Atomique (Paris, FR)
|
Appl. No.:
|
690001 |
Filed:
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April 23, 1991 |
Foreign Application Priority Data
Current U.S. Class: |
34/443; 34/107 |
Intern'l Class: |
F26B 003/00 |
Field of Search: |
34/22,23,15,29,151,148,107
|
References Cited
U.S. Patent Documents
4236851 | Dec., 1980 | Szasz.
| |
Foreign Patent Documents |
224034 | Jun., 1987 | EP.
| |
346224 | Dec., 1989 | EP.
| |
Other References
IBM Technical Disclosure Bulletin, 22(5), 1864-65 (1979) "Diverted flow
Bernoulle Pick-up Device", Balder and Cachon.
|
Primary Examiner: Bennet; Henry A.
Attorney, Agent or Firm: Meller; Michael N.
Claims
We claim:
1. Process for the protection of surfaces (11) of objects (10) against
ambient particulate contamination by confinement of the objects (10) in an
ultra-clean air atmosphere by means of blowing elements (25,32,33,38)
distributing the ultra-clean air through air distribution orifices (6,36)
issuing by a blowing surface (7) into a space where the objects (10) to be
confined must be placed, characterized in that the blowing surface (7) by
which issue the orifices (6,36) has a shape complementary to that of at
least the periphery of the surfaces (11) to be protected and it consists
of placing said surfaces (11) at a relatively short distance (d) from the
blowing surface (7), so that the flow of ultra-clean air in the volume
formed by the surfaces (11) to be protected and the blowing surface (7),
positioned in parallel facing manner, is laminar, at least at the
periphery of the object to be protected.
2. Process according to claim 1, characterized in that the surfaces (11) to
be protected of the objects (10) are centered with respect to the orifices
(6,36).
3. Process according to claim 1, characterized in that it consists of using
several blowing elements (25,32,33,38) placed end to end in order to form
a continuous ramp serving to confine the surfaces (11) to be protected
during the transfer of the objects (10) from one end to the other of the
ramp.
4. A blowing element which will protect the surfaces (11) of the objects
(10) against ambient particulate contamination by confinement of the
objects (10) in an ultra-clean air atmosphere by means of blowing elements
(25, 32, 33, 38) which will distribute the ultra-clean air through air
distribution orifices (6, 36) which issue by a blowing surface (7) into a
space where the objects (10) to be confined must be placed, characterized
in that the blowing surface (7) by which issue the orifices (6, 36) has a
shape complementary to that of at least a periphery of the surfaces (11)
to be protected and it consists by placement of said surfaces (11) at a
relatively short distance (d) from the blowing surface (7), so that the
flow of ultra-clean air in the volume formed by the surfaces (11) to be
protected and the blowing surface (7), positioned in parallel facing
manner, is laminar, at least at the periphery of the object to be
protected.
5. Blowing element according to claim 4, characterized in that it is
longitudinal (32,33) and that the central orifices are constituted by a
longitudinal slot (36).
6. Blowing element according to claim 4, characterized in that it is round
(25) and in that the central orifice is constituted by a single central
orifice (26).
7. A blowing ramp which is characterized by the use of several blowing
elements (25, 32, 33, 38) placed end to end in order to form a continuous
ramp serving to confine the surfaces (11) to be protected during the
transfer of the objects (10) from one end to the other of the ramp,
characterized in that it comprises several blowing elements assembled with
one another and each constituted by a plate (2) having a blowing surface
(7) and at least one central orifice (6, 26, 36), a pipe (4,24, 34) fixed
to the plate (2) issuing laterally into the orifice (6, 26, 36) and which
can be connected to an ultra-clean air source, certain blowing elements
(32, 33) being longitudinal, their central orifices being constituted by a
longitudinal slot (36), other blowing elements (25) being round and having
a single central orifice (26) and so as to constitute a blowing ramp
adaptable to the path covered by the objects (10) carrying the surface
(11) to be protected, the various blowing elements being placed end to
end.
8. Blowing ramp according to claim 7, characterized in that it comprises at
each end, end elements (38) having a transverse pipe portion for forming a
transverse air curtain.
9. Blowing element according to claim 4, characterized in that each pipe is
completed by a baffle plate (9) positioned facing the supply ducts (8)
issuing into the pipes (4,24,34) in order to improve the distribution of
the ultra-clean air throughout the pipe (4,24,34).
10. A blowing element in accordance with claim 4 which will protect
surfaces (11) of objects (10) against ambient particulate combination by
confinement of the objects (10) in an ultra-clean air atmosphere by means
of blowing elements (25, 32, 33, 38) distributing the ultra-clean air
through distribution orifices (6, 36) issuing by a blowing surface (7)
into a space where the objects (10) to be confined must be placed,
characterized in that it comprises a plate (2) having a surface
constituting the blowing surface (7) and incorporating at least one
central orifice (6, 26, 36) and a pipe (8, 24, 34) fixed to the plate (2)
issuing laterally into the orifice (6, 26, 36) and connectable to an
ultra-clean air source.
Description
DESCRIPTION
1. Field of the Invention
The invention relates to the storage and in particular the transportation
or conveying of parts, whereof one surface has to be kept in an
ultra-clean environment. It more particularly applies to the protection
against ambient particulate contamination or pollution of silicon wafers
during their conveying.
2. Prior Art
During the manufacture of integrated circuits, the silicon wafers
supporting said circuits are stored in loading and unloading stations.
They are conveyed by appropriate conveying means, such as air cushions,
belt conveyors and vacuum grippers. These displacements take place between
the different treatment stations, which can be a reactor, an oven or an
isolator. The wafers can then be stored again. The various treatment
stations are in an ultra-clean, non-polluting environment for the silicon
wafers. However, a contamination by dust is still possible during
conveying, unless special environmental precautions are taken.
In order to solve the problem of contamination during the movement of the
silicon wafers to the stations, conveying means are normally placed in a
rigid, matched tube, which is subject to a non-polluting air flow. This
solution suffers from the major disadvantage of requiring a means which is
adapted once and for all to the equipment and which is difficult to apply
to all transportation cases encountered during the movement of silicon
wafers.
In addition, French patent application No. 2 632 617 discloses a passage or
channel appropriate for the conveying of parts in an ultraclean
environment. This passage comprises a first type of horizontal unitary
elements constituted by unitary ducts having nozzles and an attachment
system. Two air-permeable, flexible lateral skirts are constituted by a
second type of vertical unitary elements. As the horizontal ducts are
connected to a pressurized air source, the nozzles project said air into
the passage constituted by the horizontal unitary ducts and the lateral
elements forming the skirt. These elements are assembled with one another
so as to match the geometry of the path to be protected. The passage
serves to protect silicon wafers against pollution during their
transportation. This type of passage can be effective in maintaining an
ultra-clean environment, but involves significant air flows.
The object of the invention is to supply means for protecting silicon
wafers during their conveying using the technique of blowing pressurized
air, but whilst avoiding the aforementioned disadvantage.
SUMMARY OF THE INVENTION
Therefore a first object of the invention is a process for protecting the
surfaces of objects against ambient particulate contamination, by
confining the objects in an ultra-clean air atmosphere by means of blowing
elements distributing the ultra-clean air through air distribution
orifices issuing by a blowing surface into a space in which is placed the
objects to be confined.
According to the invention, the blowing surface by which the orifices issue
has a shape complementary to that of at least the periphery of the
surfaces to be protected, the inventive process consisting of placing the
surfaces to be protected at a relatively short distance from the blowing
surface so that the flow of ultra-clean air from the orifices occupies the
volume defined by the surfaces to be protected and the blowing surface
positioned facing one another and so that said flow is of a laminar
nature, at least on the periphery of the object to be protected.
The efficiency of this process is increased when the surfaces of the
objects to be protected are centered with respect to the orifices of the
blowing surface, so that the air flow is symmetrical. It is consequently
possible to store below the blowing surface objects, whose surfaces to be
protected have a shape complementary to that of the blowing surface.
In order to adapt this process to the transportation or conveying of
objects, a preferred embodiment of the invention consists of using several
blowing elements placed end to end to constitute a continuous ramp and
which serves to confine the surfaces to be protected during the conveying
of the objects from one end of the ramp to the other.
In order to realize the process according to the invention, a second object
thereof is a blowing element having a plate with a surface constituting
the said blowing surface onto which issues at least one central orifice
and a pipe fixed to the plate issuing laterally into the orifice and which
can be connected to an ultra-clean air source.
These blowing elements are given two main constructional forms namely a
longitudinal form, the blowing element being a longitudinal slot and a
round form with a single central orifice in the blowing element plate.
With a view to obtaining a ramp adaptable to the path covered by the
objects whose surfaces are to be protected, it is possible to use several
longitudinal elements placed end to end in order to constitute straight
line portions of a blowing ramp, the direction changes of said blowing
ramp being ensured by round elements.
A preferred variant of a thus formed ramp provides for the elements
constituting the ends having a transverse pipe portion forming a
transverse air curtain at the outlet from the blowing ramp.
BRIEF DESCRIPTION OF DRAWINGS
The invention is described in greater detail hereinafter relative to
non-limitative embodiments and the attached drawings, wherein show:
FIG. 1 a straight line element of a means for conveying silicon wafers to
which the present invention applies.
FIG. 2 a direction change device for the conveying means of the silicon
wafers to which the invention applies.
FIG. 3 a longitudinal element used in the process according to the
invention.
FIG. 4 a cross-section through the longitudinal element of FIG. 3.
FIG. 5 a round element used in the process according to the invention.
FIG. 6 an embodiment of a ramp end element according to the invention.
FIG. 7 an example of the assembly of two longitudinal elements of the ramp
according to the invention.
FIG. 8 a plan view of a ramp according to the invention with a direction
change.
FIGS. 9A and 9B a constructional variant of a round element used in the
process according to the invention.
DETAILED DESCRIPTION OF AN EMBODIMENT
The conveying means for flat objects, such as silicon wafers, shown in FIG.
1 is a path or track 14 having air jet ducts 15 issuing obliquely in the
longitudinal direction, so as to advance the silicon wafer 10. This track
14 is positioned at the outlet of a case 12 in which are arranged several
silicon wafers 10.
There are also other means for conveying the silicon wafers 10. Thus, it is
possible to use conveyors constituted by two horizontal, parallel belts
moving horizontally in the same direction.
These two conveying means types make it possible to cause the silicon
wafers to carry out straight line displacements. However, in most uses of
such silicon wafer conveyors, it is necessary to make direction changes
during the conveying of said wafers.
FIG. 2 shows one of the direction change devices, which consists of placing
a suction gripper 21 in the vicinity of a track 14. The gripper is
constituted by a base block 16 fixed with respect to the track 14 and
supporting a vertical rotary shaft 17. On the latter is mounted a
pantograph-type articulated system 18, whereof a first apex is fixed to
the shaft 17 and whereof the second apex is equipped with a suction
device. The complete opening out of the pantograph 18 enables the suction
device 19 to move above the track 14 in order to take up a silicon wafer
10. The bending back of the pantograph 18 makes it possible to bring the
silicon wafer above the base block 16. This is followed by a rotation of
the rotary shaft 17 by an angle .theta. corresponding to the angle formed
by the direction of the upstream track 14 and the downstream track, which
is symbolized in FIG. 2 by a case 12. The pantograph 18 is then opened out
again to place the silicon wafer 10 in the case 12.
The protection process and the various elements which it uses are described
hereinafter.
The element shown in FIG. 3 is a longitudinal blowing element used for
forming a blowing ramp. It is constituted by a planar plate 2 forming a
blowing top. It has orifices 6 issuing onto its lower surface 7, which is
therefore a blowing surface. A pipe 4 is fixed to the upper surface 5 of
the plate 2 facing the central orifices 6. The pipe 4 shown in FIG. 3 has
a semicylindrical shape. However, this only constitutes an exemplified
embodiment, the result necessary for the efficiency of the process being
that said pipe 4 supplies the central orifices 6 with air. The supply of
said pipe 4 with ultra-clean air can be obtained by means of ducts 8
issuing into the said pipe 4. The central orifices 6 are generally
constituted by a single longitudinal slot.
As shown in FIG. 3, a silicon wafer 10 is placed just below the blowing
element.
FIG. 4 shows in greater detail the position of the silicon wafer 10 with
respect to the longitudinal element 1. Thus, the silicon wafer 10 is
placed at a distance d of approximately 1 mm. More precisely, in the case
of the application to silicon wafers, said distance is generally between
0.5 and 3 mm. It is clear that the ultra-clean air issuing from the pipe 4
by the orifices 6 also strikes the surface to be protected of the silicon
wafer 10. In a preferred, but non-limitative manner, the latter is
positioned symmetrically with respect to the orifices 6, so that the
ultra-clean air issuing from these orifices 6 of the blowing surface 7 is
distributed in an equal manner on both sides of the volume formed by the
blowing surface 7 and the upper surface 11 to be protected of the silicon
wafer 10.
Each pipe 4 can be internally supplemented by a baffle plate 9 in FIG. 4.
The latter is positioned facing the supply orifices 8 issuing into the
upper part of the pipe 4. The baffle plate 9 lengthens the path of the
ultra-clean air in the pipe 4 in order to improve the distribution of the
latter throughout the volume of said pipe 4. This has the effect of making
the air flow in the longitudinal slot 6 more uniform.
With a view to obtaining a laminar flow in said volume, i.e. a regular flow
without turbulence and without an opposing air stream, the orifices 6 can
be given a particular shape. As shown in FIG. 4, the orifices 6 can be
constituted by a longitudinal slot preferably having a V shape within the
pipe 4. The final spacing e of the longitudinal slot is preferably between
0.3 and 2 mm.
It is pointed out that the distance d separating the silicon wafer 10 from
the blowing surface 7 and the spacing e of the longitudinal slot formed by
the orifices 6 condition, with the diameter D of the silicon wafer 10, the
ultra-clean air flow rate Q. Thus, the latter must assume a value between
a minimum and a maximum flow rate. The minimum flow rate is that for which
the air can still sweep the entire surface 11 of the silicon wafer 10 and
pass out of the periphery thereof. The maximum flow rate is just below
that where the ultra-clean air flow becomes turbulent.
The plate 2 is also dimensioned as a function of the diameter D of the
silicon wafer 10. It is necessarily wider than the diameter D of the
silicon wafer 10, said width preferably being equal to D.times.6/5.
For silicon wafers with a diameter D equal to 150 mm, a spacing e of the
longitudinal slot equal to 0.5 mm, a distance d from the silicon wafer 10
to the plate 2 of 3 mm, the contamination of the wafers conveyed beneath
these elements is at a minimum for a flow rate of 2 to 3 m.sup.3 /h.m of
the thus formed blowing ramp. It is therefore preferable in this case to
have a flow rate of approximately 5 m.sup.3 /h.
With the aid of the operating conditions referred to in the previous
paragraph, a calculation involving the use of the Reynolds R number and
the kinematic viscosity of the air .nu. makes it possible to check the
laminar state of the air flow between the two parallel surfaces.
The mean velocity V.sub.m is equal to V.sub.m =Q/S, Q being the flow rate
intercepted by a silicon wafer subject to a flow rate of 5 m.sup.3 /h.m.
The flow rate intercepted by a silicon wafer is consequently equal to
1.Q.times.D/L, D being the diameter of the silicon wafer and L the length
covered. Therefore the flow rate intercepted by a wafer of diameter 6"
(150 mm) is equal to 5.times.0.15:1=0.75 m.sup.3 /h.
The air volume passing out of one side of a silicon wafer is consequently
0.375 m.sup.3 /h through an outlet cross-section of D.times.d, i.e.
0.45.times.10.sup.-3 m.sup.2. The issuing velocity V.sub.m is equal to
0.375/3,600.times.1/0.45.10.sup.-3, i.e. approximately 0.23 m/s. Therefore
the Reynolds R number is equal to V.sub.m .times.e/.nu. of
23.times.3.10.sup.-1 /15.10.sup.-2, i.e. approximately 50.
For a flow between two parallel planes, it is accepted that when the
Reynolds R number is below 1400, perfectly laminar conditions exist, i.e.
the case of the previous example.
FIG. 5 shows a circular blowing element. Its structure and operation are
identical to those of a longitudinal blowing element. The fundamental
difference compared with the longitudinal element are that the pipe is
reduced to a simple hemispherical shape 24. It is applied to a circular
plate 25 above a central orifice 26 and is supplied by a duct 28 connected
to an ultra-clean air source.
The flow of air through the central orifice 26 takes place in an identical
manner to the flow obtained with a longitudinal blowing element, i.e. said
flow is symmetrical with respect to the centre of the circular plate 25
and remains laminar.
With reference to FIG. 6, it is possible to envisage different
constructions of the longitudinal blowing elements. It is possible to see
in FIG. 6 a rectangular pipe 34, which is supplied by ducts 8 connected to
a pressurized ultra-clean air source.
In the case where the longitudinal element 32 constitutes the end of a
blowing ramp, it can be equipped with an end element 38 constituted by a
transverse pipe portion connected to the pipe 34 by a lateral opening 39
positioned in the centre of the pipe 38. In an identical manner to the
pipe 34 of the longitudinal element 32, pipe 38 has a slot 36 identical to
that described relative to FIGS. 3 and 4. Thus, said pipe can also be
supplied with ultra-clean air, a transverse air curtain providing a
supplementary protection for the silicon wafers against contamination.
The most advantageous use of the invention consists of forming a blowing
ramp having for the straight portions longitudinal elements 32 and for the
direction changes round blowing elements, in the manner described relative
to FIG. 5.
With reference to FIG. 7, the different longitudinal blowing elements 32
can be assembled by locking edges or sides 40. The latter are positioned
transversely and vertically with respect to the plates 2 at each end
thereof. If appropriate, said edges can seal the pipes 34. The
longitudinal elements 32 are assembled by moving together engaging the
transverse edges 40 located at the respective ends of the longitudinal
elements and maintaining them together by locking and adhesion.
The embodiment described only constitutes an example. Thus, they can be
placed end to end and held together by a complementary adapting part 42
forming a pipe portion. This intermediate part 42 is inserted in the
respective ends of the pipes 34 of the two longitudinal elements 32.
FIG. 8 is a plan view of a blowing ramp using first longitudinal blowing
elements 32 and a circular blowing element 25 for carrying out a direction
change between two straight line portions. Other longitudinal elements 33
are used for forming the joint between the longitudinal blowing elements
32 and the circular blowing element 25. These second longitudinal blowing
elements 33 have a concave, circular cut end 35 complementary to the outer
shape of the circular blowing element 25.
As shown in FIGS. 9A and 9B, it is possible to envisage a constructional
variant of the round blowing element. Thus, it is possible for the shape
of the blowing surface 7 of the blowing element to only be complementary
over part of the surface 11 to be protected. As the inventive concept is
based on the fact of creating a laminar ultra-clean air flow on the
surface 11 to be protected, so that no polluting particles can enter on
the side of the surface 11 to be protected, it is possible to limit said
laminar flow to the periphery of said surface 11. Thus, as shown in FIG.
9A, the blowing surface 7 is only parallel to the surface 11 to be
protected on its periphery. The remainder of the blowing surface can be
constituted by a cone 44 directly connecting the duct 28 to the blowing
surface 7. The ultra-clean air is symmetrically distributed in the thus
defined pyramidal volume. The laminar flow takes place in the peripheral
portion, i.e. when the ultra-clean air is confined between two portions of
parallel surfaces.
FIG. 9B is a plan view corresponding to FIG. 9A. The crown-shaped zone 46
corresponds to the zone where the ultra-clean air flow is laminar. In view
of the thickness variation between the surface 11 to be protected and the
blowing element, the velocity of the ultra-clean air is virtually zero in
the centre of said element when it passes out of the duct 28. As the
thickness decreases, the velocity of the flow increases, as symbolized by
the radially oriented vectors in FIG. 9B. In this case the blowing element
must have a diameter larger than the diameter D of the surface 11 to be
protected and in the present case a diameter of 6D/5.
In this case, the air flow and the distance d separating the two surfaces
at their periphery also contribute to forming a protective curtain having
an efficiency equivalent to that of the previously described
constructions.
Thus, it is possible to construct blowing ramps adapted to any random path
of objects having a horizontal planar surface to be protected against the
ambient contamination, the adaptation of the shape of the blowing ramp
taking place as a result of different types of blowing elements proposed,
i.e. longitudinal, round and end elements.
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